Question

Can microorganisms be seen with the naked eyes? If not, then how can they be seen?

Answer 1

The naked human eye or a normal eye with regular vision and unaided by any other tools can see objects as small as about 0.1 millimetres. A standard for measuring microbes is a micrometre. It is six times smaller than a meter or one-millionth of a meter. There are 1000000 micrometres in one meter, and it is used to measure the size of bacteria or other microorganisms. So typically, the size of microorganisms range from about one µm to about five µms.

Complete step by step answer:
Most microorganisms are tiny in size. They are very small and cannot be seen with naked eyes. A microscope is to be used to see such organisms. Hence, they are called microorganisms.
Microscopy is a technical field of using microscopes to see organisms, objects and areas of objects or organisms that cannot be seen with the naked eye. The three well-known branches of microscopy are: optical, electron, and scanning probe microscopy. X-ray microscopy is an emerging field of microscopy.
A standard microscope consists of:
a.A stage for placing the sample with a light source underneath
b.Objective lenses on a revolving turret for magnifying the sample
c.A focus dial for moving the sample up and down to get it into focus
d.An eyepiece for viewing and magnifying the sample
e.A condenser for adjusting the amount of light on the sample
The size of microorganisms or bacteria is measured in micrometres. To see these bacteria swimming, at least a 400x magnification is required. A 1000x magnification enables us to view these bacteria in more detail.

Additional Information:
For microscopy, microorganisms (e.g. bacteria) are grown in culture media. It helps in enhancing the cell division and thus in increasing their numbers.
Some common media used are:
Basal Media - e.g. nutrient broth and peptone water
Selective Media - e.g. Lowenstein-Jensen media
Transport Media - e.g. Amies medium
Enriched Media - e.g. with added blood

Note:
The cells of Thiomargarita namibiensis are large enough that they are visible to the naked eye. Thiomargarita means "sulfur pearl". The species that holds the record for the largest bacterium, Epulopiscium fishelsoni which was previously discovered in the gut of surgeonfish – grows slightly longer, but narrower.